With the rapid development of Internet and popularity of big screen multi-function mobile phones, a plenty of mobile data multimedia services have come forth and various high bandwidth multimedia services arise, such as video conference, television broadcast, video on demand, advertisement, online education, interactive game, and so on, which satisfies the growing service demand of mobile users on the one hand, and brings a new business growth point for mobile operators on the other hand. These mobile data multimedia services require that multiple users are able to simultaneously receive the same data, compared with general data services, they have characteristics such as large data amount, long duration and delay sensibility.
For effective utilization of mobile network resource, the 3rd Generation Partnership Project (3GPP) proposes the Multimedia Broadcast Multicast Service (MBMS Service) which is a kind of technique in which data is sent from one data source to multiple targets so that the network (including core network and access network) resource is shared and the utilization ratio of the network resource, especially the air interface resource, is improved. The MBMS defined in the 3GPP not only can implement low-speed multicast and broadcast of plain text messages, but also can implement high-speed broadcast and multicast of multimedia services, to provide a wide variety of video, audio and multimedia services, which undoubtedly complies with the future development trend of mobile data, and provides a better business prospect for 3G development.
In LTE, the MBMS services can adopt a multicast mode and each corresponds to one MCCH (Multicast Control Channel) and one MTCH (Multicast Traffic Channel), and the MTCH and MCCH both are logic channels. A plurality of cells send the same MBMS data on the same time-frequency resource, that is, MBMS service information or control information adopts a fashion of content synchronization, which is called MBSFN (Multicast/Broadcast over Single Frequency Network) transmission mode. A plurality of cells adopting the same physical resource (i.e., synchronization) and transmitting the same MBMS data in a MBSFN transmission mode form a MBSFN area. The MBMS services transmitting information using a multicast mode are called MBSFN services.
The MBSFN transmission mode can synchronously transmit the same content after a plurality of cells adopt the same modulated coding format, and has the following features:
1. synchronously transmitting within the MBSFN area;
2. supporting multi-cell MBMS transmission combination, that is, the user equipment performs combination of the received service information and control information of the MBMS in different cells;
3. MTCH (Multicast Traffic Channel) and MCCH (Multicast Control Channel) are mapped to a MCH transmission channel in a p-T-m (Point-To-Multipoint) mode;
4. the parameters, such as MBSFN synchronous area, MBSNF area, MBSFN transmission, advertisement and reserved cell, generally have long variation periods and are all be maintained a semi-static configuration by operation.
In this case, the UE (User Equipment) covered by a plurality of cells within the MBSFN area can receive MBMS data with the same content transmitted by the plurality of cells, and perform SFN combination for the MBMS data, so that gain of signals of the MBMS services received by the UE can be improved. In an actual LTE networking, there are a plurality of MBSFN services in one MBSFN area, and all the MBSFN services in the same MBSFN area are called a MBSFN service group, that is, a MBSFN service group corresponds to a MBSFN area. Every cell within a MBSFN area is provided with a completely same MBSFN service group. The MTCH and MCCH having a plurality of MBSFN services in the same MBSFN area can be mapped to one MCH (Multicast Channel) for multiplexing the MCH, wherein the MCH is a transmission channel.
The physical resource occupied by the MCH, i.e., the number and locations of the occupied multicast subframes, is described by MSAP (MCH Subframe Allocation Pattern) information. Generally, the MSAP information is available only within a period of time, and then the physical resource occupied by the MCH will be re-configured, wherein the available time of the MSAP information is called MSAP occasion, and generally one dynamic scheduling period corresponds to one MSAP occasion generally with a fixed length of 320 ms. A plurality of MCH and dynamic scheduling information can be transmitted in a dynamic scheduling period, and each MCH carries a plurality of MTCH and MCCH borne in each MCH. As for one MCH, dynamic scheduling information can be borne in a MAC control element or in a single logical channel MSCH (Multicast scheduling channel). The MSAP information allocates at least one subframe for the MCH, wherein the subframes transmitted in a multicast mode are called multicast subframes, and the frame containing multicast subframes is called a MBSFN frame.
Each MCH corresponds to a plurality of continuous multicast subframes. In order to improve the transmission rate of the MTCH in the MCH, a method of dynamic scheduling is used for a plurality of MTCHs borne in one MCH. By means of dynamic scheduling, two or more MTCHs can be multiplexed on the multicast subframes of the same MCH and part of or total resource of the multicast subframes can be occupied, wherein each MCH corresponds to dynamic scheduling information which is used to describe the allocation of the physical resource of each MTCH in one MCH (i.e., the occupied multicast subframes).
In the existing LTE technology, a plurality of logical channels comprising a MTCH (MBMS Traffic Channel), a MCCH (Multicast Control Channel) and a MSCH (MBMS Scheduling Channel) multiplex the MCH channel by the following way: data transmitted by different logical channels form a MAC SDU (Service Data Unit), a plurality of MAC SDUs correspond to one MAC PDU (Media Access Control Layer Protocol Data Unit), each MAC PDU corresponds to one transmission data block, while a multicast subframe corresponds to a TTI (Transmission Time Interval) within which one or more transmission data blocks can be transmitted. That is to say, data of a plurality of different kinds of logical channels can be transmitted within one multicast subframe.
To distinguish the MAC SDUs from different logical channels, identifier information is carried in MAC PDU, such as identifiers of logical channels and the location information of the data block of the logical channel in the MAC PDU, for the receiving end to distinguish data blocks of different logical channels.
In a dynamic scheduling period, the data transmitted by a MTCH continuously occupies the multicast subframe resource of the MCH channel until the service data of the service that need to be transmitted within the dynamic scheduling period are all completely transmitted. Data of different services can be transmitted within the same multicast subframe, that is, data from different services in the same MAC PDU can be in tandem connection for transmission. The above service transmission order can be notified to the receiving end through the MCCH or other signaling.
In each MSAP occasion configured in one MCH, the MCCH is borne and the control information of the MBMS service is carried, the control information indicates the control information of all the MBMS services within a dynamic scheduling period. The UE can obtain the service identifier and session identifier of the MSMB service corresponding to the MCCH, service parameters (radio bearer information, physical channel configuration information, scheduling information and so on), and actions that needs to be implemented by the UE and so on by means of reading the MCCH.
There are the following problems when the data of the MBMS services are transmitted in the MBSFN mode:
The amount of the MBMS services that need to be transmitted within different dynamic scheduling periods is also different, and accordingly, the size of the information carried by the MCCH used to describe the transmission order of each MBMS service is also different, and the physical resource occupied by the MCCH channel will be adjusted according to the size of the information carried by the MCCH.
When the UE located in a MBSFN area receives the MCH, the signals of the same MCH from different cells can be softly combined, that is, the same signals are combined. However, there is no clear definition on the location of multicast subframe occupied by the MCCH in the MCH. When the MBMS service data are transmitted through the MCH, different lower level network elements in the same MBSFN area may place the MCCH at different locations of the MCH and the allocation of the physical resource to the MCCH lacks consistency, so that the signals received by the UE from different cells are not consistent and cannot be combined, thereby reducing the user experience.